Dihydronepetalactone (DHN) is an iridoid monoterpenoid that may be represented schematically by the structure of Formula II,
and has been described by Hallahan in US 2003/0191047 (which is incorporated in its entirety as a part hereof for all purposes) as possessing a fragrance that many humans find attractive, and thus as having usefulness as a fragrance compound. Hallahan, in WO 03/079786 (which is incorporated in its entirety as a part hereof for all purposes), has also disclosed that DHN compares favorably as an insect repellent with N,N-diethyl-m-toluamide (DEET), which has been the insect repellent of choice in most commercially available insect repellents. DHN may be prepared by the catalytic hydrogenation of nepetalactone.
Various derivatives of DHN are known, among which, for example, is nepetalic acid, which may be represented schematically by the structure of Formula III,
Nepetalic acid may be isolated from the essential oil of nepeta cataria [see, for example, Eisenbraun et al, J. Org. Chem., 53(17), 3968–3972 (1988)]. Eisenbraun also teaches the treatment of nepetalic acid with an oxidizer and base to produce a dicarboxylic acid ring-opened structure (nepetalinic acid).
Nepetalic acid (Formula III) may also be beneficially synthesized by treatment of nepetalactone with strong base according to the method of McElvain et al in J. Am. Chem. Soc., 63, 1558–1563 (1941). The structure of Formula III was confirmed by Eisenbraun et al in J. Org. Chem. 46, 3303–3305 (1981).
Another derivative of DHN, as disclosed in Dawson et al, Bioorganic and Medicinal Chemistry, 4 (3), 351–361 (1996), is the ethoxy substituted variation of the structure of Formula III, represented by the structure of Formula IV
According to Dawson, op. cit., the compound of Formula IV is prepared as an intermediate in a synthetic pathway presented therein for preparing nepetalactone from R-pulegone.
In the references noted above, the respective derivatives of DHN disclosed therein are not described as being useful as insect repellents or for purposes related to fragrance, aroma or odor.
Nepetalactone, represented schematically in structure of Formula I,
is a major component of an essential oil secreted by plants of the genus Nepeta, and is the active ingredient in catnip. Although the aroma of nepetalactone is generally considered unpleasant by humans, cats find it attractive. Nepetalactone may also play a role as an insect repellent as studies of the repellency of catnip oil (predominantly nepetalactone) have shown that it was repellent towards a number of insect species on short-term exposure, but not to a number of other species [Eisner, T., Science 146:1318–1320 (1964)].
While nepetalactone and DHN are both compounds that have exhibited some degree of usefulness as an insect repellent, only DHN of the two presents a pleasing odor to humans. It is thus difficult to predict which member of the iridoid monoterpenoid family of compounds will or will not have any particular property or utility.
A need nevertheless remains to develop new compounds that will be useful as insect repellents but that will have other uses as well, some of which uses may be based on fragrance, aroma and odor. Applicants have discovered previously unknown compounds that are derivatives of DHN, and that have usefulness as insect repellents in addition to other uses based on fragrance, aroma and/or odor.